Pandas 2.0 change: Groupkey returned from groupby is a tuple instead of single value

[HansKallekleiv]

import pandas as pd

df = pd.DataFrame({"A": [1, 2], "B": [3, 4]})

for column, _ in df.groupby(["A"]):
    print(column)

Before 2.0:

1
2

After 2.0:

(1,)
(2,)

This might have some unnoticed consequences.

• Fixed one related issue in relperm module: Fix ensemble colors in relperm #1317